The present application claims priority under 35 U.S.C. xc2xa7119 to Korean Patent Application No. 1999-46227 filed on Oct. 23, 1999, which is hereby incorporated by reference in its entirety for all purposes.
1. Field of the Invention
The present invention relates to a method for dispatching lots and an apparatus for the same, and more particularly to a method for dispatching lots in which processing equipment and/or processing conditions in a succeeding process are variably arranged according to the result of a preceding process, in a semiconductor manufacturing condition in which a plurality of processes are sequentially performed with respect to a same lot, and an apparatus for the same.
2. Description of the Related Art
Generally, semiconductor integrated circuit devices using a wafer are manufactured by a number of processes such as diffusion, photo, etching, oxidation, thin film, and metal processes. The order of performing the above-mentioned processes are determined by the kind of semiconductor integrated circuit device to be manufactured, and in a predetermined processing order, the results of the preceding process directly or indirectly influences the result of the succeeding process. For example, the accuracy of the photo process significantly affects the quality of a wafer obtained by the subsequent etching process.
Further, because semiconductor integrated circuit devices are mass-produced, a plurality of identical processing equipment simultaneously performing the same functions are commonly utilized in each manufacturing process.
In such manufacturing conditions of the semiconductor integrated circuit devices, when a wafer lot dispatches from a preceding process to a succeeding process, maintaining quality and production rate become an important factor to be considered. Especially, in the case when the result of a preceding process directly influences its succeeding process, a lot dispatching which uses to its highest degree the quality relationship between the preceding and succeeding processes contributes to the improvement of quality and production rate.
In view of the lot dispatching process, it is important to determine to which equipment among a plurality of equipment in a succeeding process a wafer lot should be dispatched, as some equipment in the succeeding process maintain the level of quality obtained in a preceding process while others deteriorate or improve the quality of the wafers. Further, even identical processing equipment lack consistency in their efficiency and performance, thus resulting in inconsistent processing quality. Especially, since wafers are generally finely processed in the semiconductor manufacturing processes, a minute difference in the efficiency and performance by the equipment in succeeding processes drastically influences the quality of wafers. Thus, dispatching a wafer lot to a succeeding process having a number of processing equipment is an important matter to be considered.
In relation to the lot dispatching, it should be further noted that the most suitable processing conditions should be applied for improving the quality and productivity of wafers in a succeeding process. Respective processes have their own processing conditions to be applied for processing the wafer lots. One processing condition is a combination of various processing condition elements such as pressure, temperature, and amount of the gas. As such, the quality of wafers obtained from a process is affected largely by suitability of the processing conditions applied in the process. Hence, the processing conditions of respective processes need to be most suitably applied to obtain best quality of the wafers.
FIG. 1 shows the concept of a lot dispatching commonly applied in a semiconductor manufacturing line. Such conventional lot dispatching is classified as fixed recipe. In such lot dispatching, lots waiting to be dispatched to a succeeding process from a preceding process are dispatched at random to one of the processing equipment designated from No. 1 to No. k without particularly considering the relationship between the results of the preceding process and/or the performance characteristics of the succeeding processing equipment. Such conventional random dispatching relies on the experience of engineers, which can not ensure consistently good quality. Further, in the conventional lot dispatching method, the processing error of the preceding process is not systemically compensated or reduced in the succeeding process.
Further, in determining processing conditions of a succeeding process, a single fixed processing condition which does not take into account the relationship between the result of the preceding process and the manufacturing conditions required in the succeeding process has been conventionally implemented. Also, in the conventional method, if it is evaluated that the existing processing condition deteriorates quality or productivity, an engineer analyzes the cause and makes appropriate changes in the processing condition. However, control of the processing conditions is not systematically accompanied in the conventional semiconductor manufacturing process.
As a result, because of the absence of the systematic analysis with respect to the relation between the results of the preceding process and the equipment and processing conditions of the succeeding process needed for improving quality and productivity, a most suitable lot dispatching method cannot be obtained. And, due to the efficiency limit of the processing equipment and the dispersion (including the accidental dispersion) of the input elements of the preceding and succeeding processes, it is difficult to obtain a predictable constant quality and productivity. Thus, defect rate of a wafer lot tends to be enlarged as the wafer lot is processed by succeeding processes. Further, conventionally, the selection of the processing equipment and the processing condition depended on the trial and error judgement of engineers, and frequent replacement of engineers or processing equipment resulted in more inconsistencies in the manufacturing process, as can be understood in view of FIG. 1. For example, when critical dimension (CD) is utilized to analyze qualities of wafer lots in a succeeding process, inferior quality caused by the succeeding process is determined to be greater than its preceding process.
A conventional technology related to a lot dispatching method is disclosed by U.S. Pat. No. 5,841,677. The patent discloses an optimization-based dispatching rule that can be used in manufacturing a semiconductor integrated circuit using equipment that needs a batch run and/or long processing time. According to the patent, when an expected waiting time which is needed for completing the preceding process with respect to a WIP lot is longer than the allowed waiting time, the lot is instantly processed in the succeeding process. In the opposite case, WIP lots are not dispatched until the allowed lots of the preceding process arrive, rather they are dispatched after the lots are merged together with the allowed lots to become a batch.
However, the patent only discloses the fact that the preceding processing equipment is efficiently used by the dispatching rule and that the waiting time should be minimized for dispatching, and does not refer to the systematic approach about the relationship between the result of the preceding process and the equipment and process conditions of the succeeding process in regard to maintaining consistent quality and productivity.
The present invention is therefore directed to a method of dispatching lots which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.
It is a first object of the present invention to provide a lot dispatching method and system for dispatching a respective lot to a succeeding processing equipment most suitable for maintaining consistent quality, according to the systematic analytic result obtained by the relationship between the process result of a preceding process and the efficiencies and/or performance characteristics of a number of processing equipment of a succeeding process.
It is a second object of the present invention to provide a lot dispatching method and system for dispatching a respective lot processed in a preceding process to a succeeding process by applying a most suitable process condition, according to the systematic analysis obtained by the relationship between the process result of the preceding process and the process condition of the succeeding process.
It is a third object of the present invention to provide a lot dispatching method and system for dispatching a respective lot processed by the preceding process to a succeeding processing equipment most suitable for improving the quality of the lot by applying a succeeding process condition most suitable for quality improvement, according to the systematic analysis obtained by the relationship between the process result of the preceding process and the efficiency and/or performance characteristics of a number of equipments and the process condition of the succeeding process.
In order to achieve the first object of the present invention, there is provided a first lot dispatching method for dispatching a first lot which has been processed by a first processing equipment using a first process to a second process posterior to the first process in which a plurality of second processing equipment are operated in parallel. The first lot dispatching method includes the steps of: storing in a computer system measured data of an inspection item of second lots processed prior to the first lot by the first processing equipment and measured data of the inspection item of the second lots processed by one of the second processing equipment; evaluating process capabilities of the plurality of second processing equipment which compensate the deviations from a target value of the inspection item which are generated by the first processing equipment with respect to the first lot to the target value of the inspection item based on the accumulated measured data and determining a dispatching order of the first lot to be dispatched to the plurality of second processing equipment according to the evaluated process capabilities by the computer system; and dispatching the first lot to one of the second processing equipment available which is designated by the dispatching order.
The lot dispatching method may further comprise the steps of measuring respective inspection items of a lot respectively processed by the first and second processing equipment, and transferring the measured data obtained from the respective inspection items to the computer system and updating the existing data stored in the computer system.
The process capability of the second processing equipment is represented by a span of the inspection item that is calculated by the following equation, and dispatching order is determined by its absolute value.
Span=Axe2x88x92(R+TG)
where the parameter A is a measured value of the inspection item of the first lot, and the parameter TG is a target value of the inspection item of the second process, and the parameter R is a latest representative value of skews generated by each pair of processing equipment comprised of the first and second processing equipment, and the skews are deviation values between the measured value of the inspection item of the first process and the measured value of the inspection item of second process with respect to an identical lot. The representative value R is a mean value or an average value of the skews, and the order of dispatching is determined by the absolute values of span of which a relatively low absolute value of span is given priority.
For the implementation of the first lot dispatching method, there is provided a first lot dispatching system for dispatching a first lot that has been processed by a first process to a second process in a semiconductor integrated circuit device manufacturing process having at least a first process and a second process posterior to the first process. The dispatching system includes a first stage having at least more than one same equipment for performing the first process for a second lot; a second stage having a plurality of the same equipment for performing the second process for the second lot; a measuring unit for measuring an inspection item with respect to a lot processed by the first and second processes; and a controller. The controller stores the measured data transferred from the measuring unit, and evaluates a process capability of each of the second processing equipment which compensates a deviation from a target value of the inspection item generated by the first processing equipment with respect to the first lot. Based on the evaluated process capability, the controller determines a dispatching order of the first lot to be dispatched to the second processing equipment and controls dispatching process of the first lot to one of the second processing equipment available which is designated by the dispatching order.
According to this first aspect of the present invention, respective lots having been processed by the preceding process can be dispatched to a second processing equipment by which deviations of the respective lots from the target value of the inspection item can be minimized. This is a method such that every processing equipment of a process can be most effectively used. As a result, a processing capacity, a product quality and yield can be improved markedly.
Further, in order to achieve the second object of the present invention, there is provided a second lot dispatching method for dispatching current lots in a semiconductor integrated circuit device manufacturing process having at least a first process and a second process posterior to the first process. The second lot dispatching method includes the steps of: classifying values of an inspection item into several groups according to their magnitude and preparing a plurality of process conditions for the second process each of which corresponds to each of the several groups, in which the process conditions have compensating characteristics to minimize the difference between a standard value of a group corresponding to the process condition and a target value of the inspection item; measuring the inspection item with respect to the current lots after the first process; selecting one process condition corresponding to a measured value obtained in the measuring step among the plurality of process conditions; and dispatching the current lots to the second process with setting of the second process to a selected process condition.
The second lot dispatching method may further include the step of selecting an object lot of which a measured value of the inspection item satisfies a product standard but does not satisfy a control standard from current lots processed by the first process for being applied to the lot dispatching method, in which the product standard is an external criteria for judging whether a lot is defective or non-defective in a product quality and the control standard is set more strictly than the product standard.
Introducing of the plurality of process conditions is realized by the steps of: selecting one or more process condition elements which influence process result with respect to the inspection item among process condition elements of the second process; determining a function for regulating the values of the inspection item, the selected process condition elements being parameters of the function; determining values of the parameters for compensating the differences corresponding to respective groups; and setting the values of the parameters as values of the process condition elements. Preferably, the process condition element, which becomes a parameter of the function, is selected from a plurality of process condition elements by which dispersion characteristics of the measured value with respect to the inspection item is obtained within a predetermined reference range. It is preferable that the function is substantially linear with respect to the parameter.
Further, for the implementation of the second lot dispatching method, there is provided a second lot dispatching system for dispatching a current lot which has been processed by a first process to a second process in a semiconductor integrated circuit device manufacturing process having the first process and the second process performed after the first process. The second lot dispatching system includes a measuring unit for measuring an inspection item of the current lot and a second processing equipment for performing the second process for the current lot, and a controller. The controller classifies values of the inspection item into a plurality of groups according to their magnitudes, and prepares a plurality of process conditions corresponding to the groups for the second process. The process conditions have compensating characteristics which minimize a difference between a standard value of a group corresponding to the process condition and a tar get value of the inspection item. The controller further selects a process condition among the process conditions based on a magnitude of the measured data transferred from the measuring unit, and dispatches the current lot to the second process with setting of the second process to the selected process condition.
According to the above-mentioned second aspect of the present invention, a plurality of processing recipes are flexibly and optimally applied in the succeeding process based on the process quality of the preceding process. An optimal processing recipe can reduce the deviation between a reference value of a respective group and a target value of the inspection item, which results in increase of processing capacity and various advantages such as reduction of cost and time and increase of quality and yield.
In order to achieve the third object of the present invention, there is provided a third lot dispatching method. This method is obtained from integration of the first and second lot dispatching methods. For dispatching a current lot which has been processed by a first processing equipment by a first process to a second process posterior to the first process in which a plurality of second processing equipment are simultaneously operated, the third lot dispatching method includes the steps of: measuring an inspection item of lots processed by the first processing equipment and an inspection item of lots processed by a second processing equipment; classifying values of the inspection item into several groups according to their magnitude and preparing a plurality of process conditions for the second process, in which the process conditions have compensating characteristics which minimize a difference between a standard value of the group corresponding to each of the process conditions and a target value of the inspection item; determining whether the measured value of the inspection item of the current lot is a first case in which the measured value satisfies a product standard but does not satisfy a control standard set more strictly than the product standard or a second case in which the measured value satisfies the control standard; selecting one process condition among the plurality of the process conditions based on the measured value of the inspection item of the current lot if the current lot is determined to be the first case, and dispatching the current lot to the second process while setting the second process to the selected process condition; and dispatching the current lot to a second processing equipment which compensates deviations from the target value of the inspection item generated by the first processing equipment with respect to the current lot to a smallest value if the current lot is determined to be the second case.
There is also provided a third dispatching system suitable for implementing the third lot dispatching method which serves to dispatch a first lot which has been processed by a first process to a second process posterior to the first process in a semiconductor integrated circuit device manufacturing process having the first process and the second process. The third lot dispatching system has a first stage having at least one same first processing equipment for performing the first process on a second lot by using the first processing equipment; a second stage having a plurality of the same second processing equipment for performing the second process on the second lots; a measuring unit for measuring the inspection item of lots processed by the first and second processes; and a controller.
The controller stores measured data received from the measuring unit, classifies values of the inspection item into a plurality of groups according to their magnitude, and prepares a plurality of process conditions corresponding to the groups for the second process. Especially, the process condition has compensating characteristics that minimize the difference between the standard value of the groups corresponding to the process condition and the target value of the inspection item. Further, the controller judges whether the measured value of the inspection item of the first lot is a first case in which the measured value satisfies the product standard but does not satisfy the control standard set more strictly than the product standard and a second case in which the measured value satisfies the control standard. When the first lot is judged to be in the second case, the controller evaluates the process capabilities of the second processing equipment which compensate the deviation from the target value generated by the first processing equipment with respect to the first lot to the target value of the inspection item according to the stored measured data, determines the dispatching order of the first lot with respect to the plurality of second processing equipment according to the evaluated process capability, and dispatches the first lot to one of the second processing equipment available which is designated by the dispatching order. Further, when the first lot is judged to be in the first case, the controller selects one process condition from the plurality of process conditions based on the magnitude of the measured data transferred from the measuring unit and dispatches the first lot to the second process with setting of the second process to the selected process condition.
According to the third aspect of the present invention, when a lot processed by the preceding process has a small deviation between the measured value of the inspection item and the target value, optimizing of the process equipment of the succeeding process is applied to reduce the deviation of the lot. Further, when the deviation of the lot has a large value, optimizing of the process recipe of the succeeding process is applied to reduce the large deviation. Therefore, in spite of the magnitude of the deviation value, the third aspect of the present invention can always urge the quality of the lot to move toward the target quality process by process.
These various aspects of the present invention can be applied to overall processes of the semiconductor device-manufacturing factory, which will result in a remarkable increase of a whole production capacity of the factory.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.